This project will examine the development of sleep state organization and physiological measures that define sleep states in normal infants and infants at risk for the sudden infant death syndrome (SIDS). Two groups at risk for SIDS, infants who later succumbed to SIDS and siblings of SIDS victims, will be compared with age-matched controls using data already collected. The objective is to determine if disturbed patterns of sleep state organization previously observed in SIDS siblings are also present in infants who subsequently succumbed to SIDS. Twelve-hour portions of twenty-two 24-h ambulatory recordings of SIDS victims and 66 recordings of control infants will be subjected to machine classification of sleep state. The temporal characteristics of sleep-waking states, including total state time, distribution of state epoch duration, state transition probabilities, and periodic organization, will be compared between these two groups and with 12-h observer-classified recordings of SIDS siblings an age-matched controls. The temporal organization of physiological variables that define sleep states will also be assessed using both time domain filtering procedures and frequency domain spectral techniques to determie if rapid alterations in activity are diminished in infants at risk. Relationships of cyclic alterations in activity to 3-4 h "feeding" rhythm and to the circadian cycle will be quantified for each group. Multivariate statistical procedures, including stepwise logistic regression and discriminant analysis, will be used to assess differences among risk groups.